My invention is directed to enclosures for electrical equipment, such as motor control centers, and more particularly to a shutter mechanism which automatically closes off access to bus bars used in such enclosures to reduce the risk of inadvertent electrical contact by a technician installing or removing equipment from the enclosure.
Protecting people working within or around electrical equipment such as motor control centers against inadvertent electrical contact is a concern for designers of such equipment. A typical motor control center includes an enclosure for mounting and housing three bus bars capable of carrying high current side-by-side in the enclosure with their longitudinal axes running from bottom to top of the enclosure. A mounting panel is typically provided adjacent the bus bars and includes provisions for mounting various electrical devices, such as control units, on a mounting surface of the panel opposite the bus bars. These electrical devices and control units typically include an electrical connector for connecting the device or control unit to one or more of the bus bars. The mounting panel typically includes a connector opening over each bus bar for passage of the connector through the panel and into electrical contact with the bus bar when the electrical device or control unit is mounted on the mounting surface. While the electrical device or control unit is mounted on the mounting panel, the openings over the bus bars are typically covered by the control unit or device in a manner precluding inadvertent contact with the bus bars. Prior to installation of or the removal of the device or control unit, however, the bus bars are exposed through the openings in the mounting panel.
Many prior approaches to protecting against electrical contact have been utilized. In one approach, the bus bars are simply left exposed when an electrical device is not mounted over one or more of the connector openings in the panel, and people are simply given verbal warnings or tags are attached to the enclosure warning people against touching the exposed bus bars. This prior approach is not very satisfactory in that it really does not inhibit physical contact with exposed bus bars.
In other prior electrical enclosures, a device known as a manual shutter has been provided. The shutter typically includes a shutter panel having holes matching those of the mounting panel when the shutter is placed in an open position, so that an electrical device may be installed through the shutter and panel into contact with the bus bars. The shutters typically include one or more web areas between the holes which cover the electrical connector openings in the panel when the shutter is in the closed position. However, bus bars are exposed before the shutter is manually closed, and during any time period when the shutter has been manually opened but the electrical device has not yet been installed.
There have also been many different approaches utilized in the past aimed at providing an automatic shutter mechanism that will close on its own as an electrical device in contact with the bus bars is removed from the enclosure, without any action being taken by a technician or operator and automatically open the shutter as a replacement electrical device is inserted back into the enclosure to make contact with the bus bars. Prior approaches to providing such an automatic shutter mechanism have spanned the range from a very simple shutter operating under the force of gravity via an inclined plane, to shutters which are pushed, pulled, or otherwise forced into an open or closed position respectively upon installation or removal of an electrical device using a shutter actuation system which often includes complex arrangements of cams, levers, chains and sprockets, and the like. Such prior automatic shutter actuation systems have tended to be bulky and complex, and often extend beyond the top and bottom sides of the electrical device, thereby consuming space inside the enclosure which could more advantageously be used to mount additional electrical devices connected to the bus bars.
It is an object of my invention, therefore, to provide an improved electrical enclosure through utilization of an improved shutter mechanism. It is also an object of my invention to provide a shutter mechanism which is straight forward in its construction and operation, and very compact with little or no extension of the shutter mechanism above and below an electrical device with contacts protected by my shutter mechanism.
My invention meets the above objects by providing an improved shutter actuator including a lever having one end hinged to the shutter and extending outward from the shutter to a distal outer end of the lever configured for engaging a control unit or electrical device having electrical contacts configured to connect with bus bars within the enclosure. My improved actuator further includes a spring mechanism operably attaching the lever to the shutter for urging the distal end of the lever to pivot outward from the shutter while simultaneously urging the shutter toward a first, closed position wherein web portions of the shutter close off access to the bus bars protected by the shutter. As an electrical device is installed, a lever engaging surface of the electrical device contacts the outer end of the lever. As the electrical device is pushed into place, the lever and spring mechanism pull the shutter open to expose the bus bars for electrical connection to the electrical connectors on the electrical device. When the electrical device is removed, the spring mechanism causes the lever to pivot outward from the shutter, thereby allowing the shutter to return to a closed position.
In a preferred embodiment of my invention, a single constant force spring in the form of an extendable, coiled, tape spring is utilized for simultaneously urging the lever to spring outward and the shutter to return to the closed position. This aspect of my invention can be utilized in many different embodiments meeting the needs of a particular electrical enclosure with an elegantly simple actuator having only a few, e.g., two or three parts.
According to another aspect of my invention, an embodiment of an actuator according to my invention does not protrude above or below the top or bottom edges respectively of a control unit or electrical device connected to bus bars in an enclosure.
According to another aspect of my invention, the lever and spring mechanisms of an actuator mechanism are connected to a pusher plate operably connected to the shutter in such a manner that as the lever is pushed inward, by installing a control unit, or pulled outward by the spring, the pusher plate pushes or pulls the shutter from a closed to an open position. In a highly preferred embodiment according to this aspect of my invention, the pusher plate includes key-shaped slots for receipt of a mating key-shaped projection of the shutter. Making the operable connection between the pusher plate and shutter in this manner allows a single pusher plate configuration to be used with shutters of differing thickness or shape, thereby providing the advantage of reducing the inventory of parts which must be carried to manufacture or repair a line of equipment enclosures having different shutter configurations. The slotted shape also allows the pusher plate and shutter to be utilized on panels wherein the shutter and pusher plate are mounted for sliding movement in a different plane.
The compact size, together with simple construction and operation, allow a shutter mechanism according to my invention to be readily retrofitted into existing enclosures which formerly utilized other types of shutter mechanisms. The compact size of my shutter mechanism also makes it possible to install more equipment in the same electrical enclosure due to the fact that my shutter mechanism does not extend above or below the control unit or electrical device mounted through the shutter of my invention.
Other aspects and advantages of my invention will be apparent to those having skill in the art upon review of the attached drawings and the following detailed description.